Re: [PATCH v9 3/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit

Chao Peng
2022-11-17T13:47:48Z

On Wed, Nov 16, 2022 at 06:48:43PM +0000, Sean Christopherson wrote:
> On Wed, Nov 16, 2022, Andy Lutomirski wrote:
> >
> >
> > On Tue, Oct 25, 2022, at 8:13 AM, Chao Peng wrote:
> > > diff --git a/Documentation/virt/kvm/api.rst
> > > b/Documentation/virt/kvm/api.rst
> > > index f3fa75649a78..975688912b8c 100644
> > > --- a/Documentation/virt/kvm/api.rst
> > > +++ b/Documentation/virt/kvm/api.rst
> > > @@ -6537,6 +6537,29 @@ array field represents return values. The
> > > userspace should update the return
> > > values of SBI call before resuming the VCPU. For more details on
> > > RISC-V SBI
> > > spec refer, https://github.com/riscv/riscv-sbi-doc.
> > >
> > > +::
> > > +
> > > + /* KVM_EXIT_MEMORY_FAULT */
> > > + struct {
> > > + #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 0)
> > > + __u32 flags;
> > > + __u32 padding;
> > > + __u64 gpa;
> > > + __u64 size;
> > > + } memory;
> > > +
> >
> > Would it make sense to also have a field for the access type (read, write,
> > execute, etc)? I realize that shared <-> private conversion doesn't strictly
> > need this, but it seems like it could be useful for logging failures and also
> > for avoiding a second immediate fault if the type gets converted but doesn't
> > have the right protection yet.
>
> I don't think a separate field is necessary, that info can be conveyed via flags.
> Though maybe we should go straight to a u64 for flags.

Yeah, I can do that.

> Hmm, and maybe avoid bits
> 0-3 so that if/when RWX info is conveyed the flags can align with
> PROT_{READ,WRITE,EXEC} and the EPT flags, e.g.

You mean avoiding bits 0-2, right, bit3 is not so special and can be used
for KVM_MEMORY_EXIT_FLAG_PRIVATE.

Chao
>
> KVM_MEMORY_EXIT_FLAG_READ (1 << 0)
> KVM_MEMORY_EXIT_FLAG_WRITE (1 << 1)
> KVM_MEMORY_EXIT_FLAG_EXECUTE (1 << 2)
>
> > (Obviously, if this were changed, KVM would need the ability to report that
> > it doesn't actually know the mode.)
> >
> > --Andy